Water Blocking in Explosive Compositions

ABSTRACT

An improved non-aqueous explosive composition for usage in wet blasting environs where the described embodiments are able to provide more efficient water blocking in ammonium nitrate and fuel oil explosive compositions than the prior art. One embodiment includes an oxidizer, fuel and sodium carboxymethyl cellulose used as a water-blocking agent. Another embodiment consists of an oxidizer, fuel and hydroxyethyl cellulose as a water blocker. Other embodiments include admixtures of carboxymethyl cellulose and hydroxyethyl cellulose.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional patent application Ser. No. 61/622,529, filed 2012 Apr. 11 by the present inventor.

BACKGROUND—PRIOR ART

In the commercial explosives market for construction and mining applications, the current practice is to use ammonium nitrate and fuel oil (ANFO) primarily in dry condition and emulsions and emulsions blends in wet conditions, with some demand for slurries, water gels, and water-resistant anfo.

Water-resistant anfo is a dry, free-flowing, “coated” ammonium nitrate/fuel oil (ANFO) composition that provides protection against water, primarily for use in light and medium water conditions. It was first commercialized in the Northwest US with the earliest mention in patent literature by Sheeran (U.S. Pat. No. 3,453,155) where “guar flours” may impart desirable properties to the basic compositions. This description was not sufficient to afford protection and it soon became common knowledge in the explosive industry that guar gum could be used to increase the water-resistance of dry anfo compositions. Yancik (U.S. Pat. No. 3,640,784) followed several years later with a cross-linking system to produce a stabilizing gel in water-resistant anfo compositions. Other patents also followed in this area with Harris (U.S. Pat. No. 4,637,849) also submitting a cross-link application for usage of water resistant ANFO. Unfortunately, the use of cross-linkers did not receive general market acceptance because they increased the product costs and dramatically decreased the shelf life of the packaged final product to several months. Further developments focused on how physical aspects of the composition affected the water resistance in dry anfo compositions, including the usage of fillers and hydrophobic particles, as well as particle sizes of nitrates and other components (Richards U.S. Pat. No. 5,480,500). These additions were more useful, but were not necessarily required to still get good water resistance.

However, through the 50 history of producing and selling water-resistant anfo compositions, one thing has remained constant: the usage of guar gum flours to provide the basic water-resistance, either with or without additional enhancing techniques. No other competing water-blocking additives have been commercialized or found to be of equal or better performance.

More recently guar gum disadvantages have increased in areas primarily relating to supply, quality and pricing. Guar gum is produced from an agricultural crop that is primarily grown under monsoon rains and processed in India. As a result a successful harvest and abundant supply is highly dependent upon the monsoon weather patterns, which can often result in low quality or shortages of guar gum when rainfall is not at optimal levels. Recently, the oil industry has dramatically increased their usage of guar gum to fracture natural gas and oil well as a result of new horizontal drilling technology. This has caused a global shortage of guar and has driven up pricing an unprecedented 10-fold, causing a financial hardship on users of water-resistant anfo.

Advantages

Accordingly, an advantage of one or more aspects of preferred embodiments described herein is that water blocking can be accomplished without the usage of guar gum and in a way that is equal to or superior to the prior art.

Another advantage of one or more aspects is that the novel water-blocking material for use in water-resistant explosive compositions is “less vulnerability” to excessive spikes in price due to a well-established and substantial global manufacturing base.

Another advantage of one or more aspects of preferred explosive compositions is that the water-blocking material works well in combination with the prior art to help achieve flexibility to adapt to current market conditions.

Another advantage of one or more aspects of the water-resistant compositions is the usage of preferred embodiments result in substantial economical savings to the explosive consumer.

Further advantages will become apparent after consideration of the ensuing description.

DETAILED DESCRIPTION

Broadly speaking, this invention comprises a novel water-resistant explosive composition where water blocking is provided in a manner different from the prior art, by the novel usage of sodium carboxymethyl cellulose (CMC) or other cellulose derivatives. The usage of a suitable CMC allows for a quicker formation of a water-resisting barrier that provides for excellent water blocking in ammonium nitrate explosive compositions in a manner superior to the prior art.

More specifically, the compositions described herein include the use of an oxidizing salt. The most commonly used oxidizing salts are ammonium nitrate, sodium nitrate, and calcium nitrate. Ammonium nitrate is a preferred oxidizing salt in amounts from 75-94% with up to 50% of the ammonium nitrate being replaced by other oxidizing salts.

The compositions of preferred embodiments include the use of a fuel, which is typically a hydrocarbon petroleum liquid fuel, but other solid carbon and hydrogen fuels may also be used, such as ground coal, coke and gilsonite. The preferred fuel is #2 diesel fuel as it is commonly available and economical. Since the water-blocking elements of compositions described herein also contain carbon and hydrogen, they also may be taken into account as fuel when determining a proper oxygen balance for the explosive composition. It may be possible that high amounts of CMCs and cellulose derivatives in combination with other solid carbonaceous fuel may lower the need for liquid hydrocarbon fuels to almost zero.

The compositions of the preferred embodiments also include the use of a water-blocking additive, which is central to this invention. It has been unexpectedly discovered that excellent water-blocking results can be achieved in ammonium nitrate and fuel oil compositions with the usage of sodium carboxymethyl cellulose (CMC) or cellulose derivatives. CMCs and cellulose derivatives are manufactured from either wood or cotton, both of which are abundant and not likely to found in short supply. The manufacturing technology is generally well known and factories exist in many countries, especially the North America, Europe and the Far East capable of producing suitable CMC varieties for the preferred embodiments. CMCs are generally available in hundreds of different types, with varying characteristics in viscosities, particle sizes, degrees of substitution, purity and moisture, as well as being industrial or food quality. In fact, the sheer number of available CMC products can itself be a formidable obstacle to finding a suitable version that will work properly in the preferred embodiments.

A CMC or cellulose derivative suitable for this invention should typically have a viscosity in excess of 3000 cps as measured on a Brookfield viscometer using a #3 spindle and be of a finely divided particle size. In addition, the CMC must have good salt compatibility and be able to maintain viscosity in saturated ammonium nitrate solutions without substantial breakdown. Generally, higher degrees of substitution allow for better salt compatibility, but may not have the highest final viscosities. Therefore care must be taken in selecting the proper CMC or cellulose derivative, as both salt incompatibility and low viscosity are critical factors that can result from an incorrect selection and cause a failure in adequate water-blocking ability.

After the above mentioned elements are within tolerance, it will still be necessary to make a sample explosive composition and manually measure water resistance to determine if the CMC hydrates in a sufficiently quick manner that will function well as a water-blocker in a nitrate explosive composition. Although manufacturing processes are known and similar in making CMCs, they are not identical, and seemingly similar products from different manufacturers may still behave differently. Two CMC product suitable for providing effective water resistance is manufactured by Ashland Chemical and is sold under designations 9H4FX and 7H4FM. Other CMCs and cellulose derivatives that are close in viscosity, particle size and degree of substitution from this manufacturer will show similar results and can also be successfully used.

Although CMCs are the most common of the cellulose gums, there are other cellulose derivatives that can also be used in the same manner and function well to provide water resistance, including methyl cellulose (MC), hydroxypropyl methyl cellulose (HPC), and hydroxyethyl methyl cellulose (HEC).

A properly selected cellulose gum is able to provide water-blocking properties in the ammonium nitrate compositions by swelling quickly when coming in contact with water. But there also needs to be a sufficient percent of CMC present over the surface of the nitrate prills so that a continuous barrier capable of preventing further water penetration can be formed. The development of the barrier and it “toughness” also becomes an important element to acquire effective water blocking. For this reason the CMC also needs to be of a high viscosity type so that resulting “formed” gel barrier has sufficient integrity to continue to hold back further water impingement. Higher viscosity CMC and derivatives form denser barriers beneficial to water resistance. In the most preferred embodiments, CMCs and/or the cellulose derivatives are present in the amounts of 1.0-9% of the total weight of the explosive composition. But explosive compositions using CMCs and cellulose derivatives can still be useful even at very low percentages if only “moisture resistance” is required. And it is also possible to make effective water resistant compositions by using CMC at the high end of the preferred percentages or higher with very high additions of CMCs and their derivatives with additions up to 25%. In this case, a CMC is of low cost and low viscosity could be employed at high percentages to build sufficient viscosity and achieve water-resistance in an effort to circumvent the scope of this invention.

The actual steps in the process of actually putting together the necessary elements of preferred embodiments to produce a water resistant explosive are: 1) first coating the ammonium nitrate with 2.5-5% fuel oil and mixing thoroughly until the prills are evenly coated with fuel, and then 2) adding the desired amount of water-blocking CMC or cellulose derivative and mixing again until the prills are evenly coated. This will produce a water-resistant explosive composition with the best water-blocking results.

The following are examples that demonstrate the superior water-blocking ability of CMCs and cellulose derivatives in explosive water-resistant compositions.

EXAMPLE #1

Below is table 1-A that compares 4 sample compositions, including one composition demonstrating the capabilities of “guar only” water blocking of the prior art, and 3 additional compositions, which demonstrate preferred embodiments. The samples were prepared by mixing 89% ammonium nitrate with 5% fuel oil and 6% of a water-blocking additive, with sample #1 comprising 6% commercial quality guar gum used for water-blocking in explosives, sample #2 comprising 9h4fx CMC cellulose gum, Sample #3 a blend of a 9H4FX CMC cellulose gum and guar gum, and Sample #4 comprising 6% of hydroxyethyl cellulose as water-blocker. The samples were prepared by first: 1) combining the ammonium nitrate and fuel oil and mixing until the fuel oil evenly coats the prills, and then 2) adding the selected water-blocking materials and mixing again until the prills are evenly coated. This process was followed for composition #1, #2, #3 and #4.

The samples were then subjected to a water resistance test that simulates “light” water conditions in boreholes. The testing was performed by first placing 150 g of the selected sample compositions in round plastic cylinders 55mm in diameter and 100 mm high. Then 100 ml of water were poured within 15 seconds over the surface of the sample. After 24 hours any water not absorbed by the sample was poured off. The water-blocking barrier was then removed from the samples and the amounts of remaining dry prills were measured and recorded. Higher amounts of dry prills reflect higher water-blocking ability. Table 1-A shows the compositions of samples #1-4, which are expressed as a percent of total weight.

TABLE #1-A Sample ANFO Guar CMC-9h4f HEC Dry Prills #1 94% 6% — — 96.5 g #2 94% — 6% 100.5 g  #3 94% 3% 3% 98.1 g #4 94% — — 6% 95.3 g

Results show that in a test which simulates “light” water conditions in a borehole situation, sample #2 with a CMC water blocker gave the best results. The result of sample #3 indicates that CMC and guar in equal portions also functions better than guar alone. Sample #4 tested the water resistance of HEC as water blocker, and results showed it to be approximately equal to the guar in Sample #1.

EXAMPLE #2

In a second set of tests an independent explosive manufacturer tested the 9H4FX CMC water blocking against a commercially available water-resistant anfo mix available from Adtec Inc. in a more strenuous water resistant test that more closely simulates “medium” water conditions in a borehole. In this test the samples are lowered into a tank, which develops hydrostatic water pressure and more accurately reflects actual wet borehole conditions and the type of water blocking that is most useful and determinative.

All samples were produced by first adding 5% fuel oil to ammonium nitrate prills and mixing in the same manner as the first set of samples were created. Samples #1 and #2 were produced by adding 6% and 4.5% 9H4FX CMC respectively to the oiled prills and properly mixing. Then samples #3 and #4 were produced by adding 6% and 4.5% of Adtec's commercially available 260 premium all-guar premix to the oiled prills and properly mixing. The samples were then loaded into 1¾″ diameter tubes covered with filter paper secured at the bottom end and vertically lowered into a water tank. In this test, water is forced into the bottom of the tube covered by filter paper because of the hydrostatic pressure from being submerged in water. After several hours the compositions were removed from the tank and evaluated as to the amount of water absorbed. Results are expressed as an increase in weight, which shows the amount of water absorbed and reflects the water blocking ability of the composition. Lower percents of water absorption indicate better water-blocking ability. The results were as follows:

TABLE #2-A Sample Water Blocker Absorbed Water #1   6% CMC 2% #2 4.5% CMC 4% #3   6% Guar-260 6% #4 4.5% Guar-260 9%

The results indicate that in a more difficult testing situation that more accurately simulates actual borehole wet conditions, the CMC water blocking ability was substantially better than results from the guar-based product. In fact, an addition of only 4.5% of a CMC exceeded the water blocking results of a 6% addition of the prior art guar.

Conclusions, Ramifications and Scope of Invention

Accordingly, the above examples show that an advantage of one or more aspects is that water resistance in ammonium nitrate explosive compositions is superior to the prior art. This has significant economic advantages, especially in the current environment where the cost of the current invention is less than half the cost of the prior art on a weight basis.

The examples also show that an advantage of one or more aspects allows for the CMCs and cellulose derivatives is that excellent water resistance can be achieved without the usage of guar gum. Or, if it is becomes desirable for economic or other reasons, the CMCs and cellulose derivatives can work in blends or admixtures with the prior art. This allows the explosive manufacturer considerable flexibility in securing materials for production and to select materials that will provide the highest water-blocking at the most economical price.

Another advantage of one or more aspects of the non-aqueous water-resistant explosive compositions described herein is that the CMC and cellulose derivative water blocker are widely available from manufacturers in the global economy and are not likely to experience sharp price increases or severe shortages.

In the description of preferred embodiments were listed one or more water blocking CMCs, such as Ashland 9H4FX and 7H4FM, that are suitable and work well in the described compositions. However, these reference materials are not meant to narrow the scope of the applicable CMCs or other cellulose derivatives that function well within the described compositions. On the contrary, the above CMC are given as a positive example of what type of water blocking effectiveness can be achieved when a properly selected CMC or cellulose derivative is used in the described compositions. In fact, there are many products available in the global economy from a variety of manufacturers and countries that will function as well or possibly better than the provided reference materials and are meant to fall within the intended scope of the preferred embodiments.

In addition the scope of the described water resistant compositions should be viewed in context of the importance and far reaching effects of the novel discovery of CMCs and cellulose derivatives as effective water blockers that are able to equal and exceed the performance of the prior art, which has dominated water resistant anfo explosive compositions for the prior 50 years. Nor should the scope be easily circumvented by changing one of the many parameters pertaining to CMC and cellulose derivative manufacturing and claiming new methods, or applying prior art water-resistance enhancing techniques with hydrophobic additives, fillers, nitrate particle sizes or cross-linkers and claiming new improved products. 

I claim:
 1. A water resistant non-aqueous explosive composition, comprising; (a) an inorganic oxidizing salt from 75 to 94%, (b) a carbonaceous fuel up to 10%, and (c) a water-blocking additive comprising sodium carboxymethyl cellulose in the amount of 0.1-25%.
 2. The composition of claim 1 where the water-blocking additive is hydroxyethyl cellulose.
 3. The composition of claim 1 where the water-blocking additive is an admixture of sodium carboxymethyl cellulose and hydroxyethyl cellulose.
 4. The composition of claim 1 where the water-blocking additive is hydroxypropyl methylcellulose.
 5. The composition of claim 1 where the water-blocking additive is an admixture of the water blocking additive sodium carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl methyl cellulose.
 6. The composition of claim 1 where the water-blocking additive is an admixture of the water blocking additives sodium carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose and guar gum.
 7. The composition of claim 1 where the inorganic oxidizing salt is ammonium nitrate.
 8. The composition of claim 1 where the carbonaceous fuel is fuel #2 fuel oil, ground coal, coke, gilsonite or mixtures thereof. 